Printing telegraph private branch exchange system



April 23, 1940. J slNGER 2,198,517

PRINTING TELEGRAPH PRIVATE BRANCH EXCHANGE SYSTEM Filed' Sept. 21, 19374 Sheets-Sheet 1 SELECTOR N0. 3

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I l I l llll 0 IN [/5 N TOR By 5.]. SINGER ATTORNEY April 23, F. J.SINGER 2,198,517

PRINTING TELEGRAPH PRIVATE BRANCH EXCHANGE SYSTEM Filed Sept. 21, 1937 4Sheets-Sheet 2 SELECTOR NO. 5

E INVENTOR By E J. S/NGER mam/M W A 7' TORA/E V F. J. SINGER April 23,1940.

PRINTING TELEGRAPH PRIVATE BRANCH EXCHANGE SYSTEM Filed Sept. 21, 193? 4Sheets-Sheet 3 INVENTOR l-TJ SINGER ND 0? EQRTKW ATTORNEY April 23,1940. $|NGER 2,198,517

PRINTING TELEGRAPH PRIVATE BRANCH EXCHANGE SYSTEM I Filed Sept. 21, 1937I 4 Sheets-Sheet 4 TTV SELECTOR NO. 00

POWERJ SUPPLY (COMMON) NO. I

DUMMY S T TION INVENTOR By EJS/NGER A T TOR/V5 V POLAR/ZED Patented Apr.23, 1940 UNITED STATES PRINTING TELEGRAPH PRIVATE BRANCH EXCHANGE SYSTEMFred John Singer, Rockville Centre, N. Y., as-

signor to American Telephone and Telegraph Company, a corporation of NewYork Application September 21, 1937, Serial No. 164,922

13 Claims.

This invention relates to a printing telegraph system and moreparticularly to a small local radial telegraph system wherein theautomatic switches are employed for the establishment of 5 channels oftelegraphic communication.

The invention has for its main object to provide a telegraph privatebranch exchange system which utilizes automatically and directivelyoperable switches at a switching center for establishing telegraphicconnection between separated stations, attended and unattended, in saidprivate branch exchange and between the stations of the private branchexchangeand a public teletypewriter exchange ofiice whereby flexibility,

15 economy and efficiency are greatly increased.

Heretofore in private interconnecting systems employing printingtelegraph equipment and operating on an automatic basis, complicatedswitching mechanisms were required to establish 20 connections betweenswitches at separated stations. Considerable time was consumed inestablishing the connections particularly in the systems whereinselected rotary step-by-stp switches, that is, the two-movement, or upand.

25 around, types, were used. Furthermore, the auxiliary apparatusrequired for testing idle and busy conditions of a called station wereequally complicated and expensive;

According to the present invention no com- 30 plicated apparatus,expensive to install and maintain, is required other than a sending andreceiving printer at each station as is required in the older systemsover which the present system is an improvement. The present inventionpro- 35 vides a system wherein no more than twenty stations are presentand any two of which maybe interconnected automatically. Each station inthe system is provided with a non-locking dial key whereby a call to anystation in the system g may be initiated. A normally opened lineextending to a switching center is immediately closed by the operationof the key tothereby operate a pulsing relay. A series of relays arefrequently closed by the operation of the pulsing 45 relay to prepare acircuit for operating a rotary switch magnet whereby the rotary switchis stepped around in response to a series of dialing impulsescorresponding to the code of the called station, to a contact to whichis connected the 50 line extending to the called station. Elach stationhas associated therewith two types of cutthrough relays, one of which,referred to hereinafter as an outgoing cut-through relay, is operatedwhen its associated station is calling and 55 the other, referred toherein as the incoming cutthrough relay when its associated station isbeing called. One of each type at any two stations between which aconnection is desired, operates at the completion of dialing'to therebyconnect the calling station with the called station. Separate busy testsmay be made depending on whether the called station is busy because of acall initiated by the station itself or by another station. A disconnectsignal may be transmitted from either of two interconnected stations.The power supplies at each of the stations and at the switching centerare normally idle. One station is adapted tocomplete connections to anyof the other stations of the system or a public teletype- Writerexchange office, and in a connection so established it is possible toobtain all the super- 'Visory features of call, recall and disconnectsignaling usually provided at public teletype- Writer exchangeswitchboards.

One of the features of this invention is the use of a normally openedtransmission line connecting each of the separated stations with theswitching center of the private branch exchange system and with theoutside, or public, teletypewriter exchange ofiice. 5

Another feature is the adaptation of the invention to a demand for lowpriced teletypewriter dial private branch exchange systems which can beused with or without connections to a public teletypewriter exchangesystem and which can serve from two to twenty separated stations.

Another feature is to simultaneously establish connections between pairsof separated stations respectively, each pair ofseparated stations beinginterconnected, independently of other pairs.

Another feature is to start and stop the printer motors at both of twointerconnected separated stations from either of the interconnectedstations when both stations are attended.

Another feature is to make it impossible for a 40 calling station tointerrupt, or cut-in, on a communication between two interconnectedstations.

Another feature is to furnish additional equipment at one of theattended stations whereby any one of the other stations maybe connectedI through to a trunk circuit extending to a public ,teletypewriterexchange ofiice, the trunk circuit connections so established having allthe supervisory features of call, recall and disconnect signaling in sofar as the teletypewriter exchange switchboard is concerned asare-provided from a regular teletypewriter exchange subsc'ribersstation.

Another feature is that the equipment at an attended station equipped sothat connections may be established to a printing teletypewriterexchange ofice, provides automatic means for disconnecting the trunkcircuit at the end of a communication.

Another feature is that the selecting device is individual to eachstation in the private branch exchange.

Another featureis that the sytsem is fullautomatic with automaticcontrol of power supply for the complete system.

A preferred embodiment will now be described with respect to theaccompanying drawings which illustrate an intercommunication systemcomprising twenty stations, only four of which are shown. Each stationis equipped with type printing telegraph apparatus. The drawings arearranged into four figures:

Figures 1, to 4 respectively show the third, the fifth, the twelfth andthe twentieth stations,-each represented by a calling dial, a dial keyand a sender andreceiving telegraph printer set. Each of Figs. 1 to -4also shows the switching equipment associated with its station andlocated at a common switching center in the system. The twentiethstation; shown in Fig. 4, is further equipped with apparatus forestablishing a connection between any of the stations and a switchboardat a public teletypewriter exchange ofiice. Also in Fig. 4 is shownadditional apparatus comprising a line relay, a transformer, the primarywinding of which is connected in parallel to the printer motor and 'arectifier connected to the secondary winding of the transformer. Fig. 4further shows a trunk circuit arranged for connecting the twentiethstation and any one of the other stations to a public teletypewriterexchange munication'system serves as a dummy station and is sodesignated in Fig. 4. g Only so much of the equipment as is necessary togive a clear understanding of the invention is shown.

Referring to Fig. 1, the equipment shown to the left of the brokenportion of the line circuit comprises a sending and receiving printerset for the third station and a non-locking dial key for initiating acommunication connection, and a calling dial for completing theconnection. At the right of the broken portion of the line circuit isshown the switching equipment individual to the. third station. Theswitching equipment comprises a rotary selector switch and a group ofrelays arranged to 'be controlled from the third station. An additionalcut-through relay, referred to herein "as an incoming cut-through relay,is provided in the switching equipment, which is arranged to becontrolled from the switching equipment atone of the other stations.

'Each of Figs. 2 and 3 comprises station and switching equipment 'forthe fifth and the twelfth stations, respectively. The equipment isidentical with that shown in Fig. 1 and similarly arranged.

"Fig. 4 shows in the upper portion equipment 'for the twentieth station.The equipment is substantially identical in character and similar inarrangement 'to that shown in Figs. 1, 2 and 3 exceptv that additionalequipment is furnished at the leftof the broken portion of the linecircuit 'forestablishing connection to a public teletypewriter exchangeofiice, and the line circuit is arranged to extend through the printerset at the twentieth station to the teletypewriter exchange ofiice. Thetwentieth station may in this way be used on a monitoring basis at alltimes while the teletypewriter exchange connection is established. Fig.4 further comprises a single line repeater, a signal and an alarmdevice, control key, cutthrough relay and recall key together with theteletypewriter exchange ofiice shown in diagrammatic form in the lowerportion of the drawing. At the right side of Fig. 4 is the power supplyfor the entire intercommunication, or private branch exchange system,which comprises a control relay arranged to operate as soon as any oneof the rotary selector switches takes its first step, sources ofalternating current arranged to -be connected to two motor generatorsets when the power supply relay operates, and a rectifier forfurnishing a source of negative voltage when the'dialkey at any stationis operated to initiate the operation of the rotary selector switchassociated with the calling station. Normally the power supply isdisconnected from the system except for a slight steady drain to holdthe pulsing relays for each station normally biased, as will behereinafter described.

In a dialing system consisting of eleven to twenty stations, such asdescribed herein, the dial which is equipped to send one to ten currentimpulses each time it is operated will have to be operated twicesuccessively whenever it is desired to call a station above the firstten and, therefore, the numbering of the stations herein is showncorresponding to the number of current impulses required to call thedesired stations, for example, the numbering for the twentieth stationis 00, which means that ten must be dialed twice in order to call thetwentieth station. I

The dial key at each station isoi the non-locking type. The sending andreceiving printer set may preferably be of the start-stop type such asis disclosed in United States Patent 1,745,633 granted'to S. Morton etal. on October 4, 1930.

The system is normally in the position shown. 'All relays are normallydeenergized except the pulsing relays for each station, which relays arenormally energized by a biasing current flowing through their lowerwindings. Assuming that it is desired to connect the printer set at thethird station, No. 3, to the printer'set at the fifth station, No. 5,and that station'No. 5 is not busy, the attendant at station No. 3operates dial key Elli. A circuit is closed from a grounded source ofnegative potential at rectifier 549, conductor 55i, through the upperwinding of pulsing relay Hi2, conductor h 3 back contact and outer upperarmature of outgoing cut-through relay i ll, back contact and upperarmature of incoming out through relay Hi5, line conductor we,make-before-break contact of key Hi1, upper contact of dial I01, throughthe winding of polarized relay I08, break contact of relay Hi9, lowercontact of dial it? to ground. The armature of pulsing relay I02 whichis normally held against its lefthand contact by, the biasing currentflowing from the negative side of rectifier through the lower winding ofrelay 102 through resistance I i G to ground, moves to. its rightcontact. Closure of, dial key it: disconnects the printer set comprisingtransmitter ii! and receiver H2 from the line circuit. The currentthrough the polarized relay IE8 is in 'such'a direction at this time,that is, with negative potential on the tip side conductor liifi, of theline circuit, that the relay iii) does not operate. The operation ofrelay I02 to its right-hand position causes slow-release relay I I3 tooperate in a circuit traceable from ground on the winding of relay I I3,conductor H4, right contact and armature of relay I02, conductor H5,outer upper armature and contact of relay HB, back contact and innerupper armature of relay I I1, conductor I I8 to the grounded negativepotential conductor 45!. Relay H3, in operating, closes an operatingcircuit for relay H9 which circuit is traceable from ground, through thewinding of relay H9, contact and armature of relay I I3, groundednegative potential conductor 45L Relay H9, in operating, opens at itsinnermost lower armature and contacts a circuit extending through thelower winding of relay I 20 and prepares at its middle lower armatureand contact a circuit from the grounded negative potential conductor 45Eto the ring conductor 5 2i of the line circuit, which prepared circuitwill later be established when the outgoing cut-through relay IIloperates. Relay H9, in operating, also prepares at its outermost lowerarmature and front contact an operating circuit for the stepping magnetI22 of selector switch No. 3, which circuit is now open at the armatureand left-hand contact of relay I02, and closes an operating circuit forrelay I23 which operates. Relay I23, in operating, breaks at itsarmature and back contact, the connection between the wiper of selectorbank B3 and the upper winding of relay I20 and prepares at its armatureand front contact a circuit extending over the front contact and innerupper armature of relay II'I, conductor H8 to the grounded negativepotential conductor 45 I.

Selector switch No. 3 is now prepared to receive diel pulses from dialI01. The attendant at station 3 dials station No. 5 and pulsing relayI02 will be released five times and then operate at the end of theperiod. When relay I02 releases the first time, slow-release relay I24and the stepping magnet i22 will operate in series, the operatingcircuit being traceable from the grounded negative potential conductor45!, conductor H8, inner upper armature and back contact of relay II'll, contact and outer upper armature of relay H6, conductor H5,armature and left-hand contact of-relay I02, through the winding ofrelay I24, conductor I25, front contact and outermost lower armature ofrelay H9, through the winding of stepper magnet I22, lower armature andback contact of relay H6, conductors I20 and I 27, normal contact, thatis, contact No. 22, of bank E3 engaged by its associated wiper,conductor I28 to ground at the break contact of relay I 24. When relayI02 operates to its right hand contact in response to the second pulsethe current supply will be removed from the windings of relay I24 andstepping magnet I24. Relay I22 being of the slow-release type willremain operated, but the stepping magnet I22 will release therebycausing the wipers of selector switch No. 3 to step from theirrespective contacts No. 22 to their respective contacts N0, 1 on thefive banks shown.

When relay I02 releases the second time the stepping magnet I22 willagain operate and this time the selector wiper on bank E3 is on contactNo. l and relay I24 is operated so that the operating circuit for thestepping magnet is established directly through the armature and frontcontact of relay I24 and not over the wiper of bankEs as previouslytraced. Relay I02 in operating the second time causes the selectorwipers to step to their respective contacts No. 2. This sequence isrepeated during the remaining dial pulses, the selector wipers steppingto their respective contacts No. 5. when relay I02 operates at the endof the series of pulses. It is to be noted that during the time theselector wipers are stepping, the wiper circuit extending through bankB3 is held open at the front contact and inner upper armature of relay II! thus preventing interference with other circuits on the multiples ofthat bank. The wiper on bank A3 has grounded negative potential appliedto it during the second interval from contact bank D3, but this appliedpotential meets a similar potential on each point through the multiplesto each respective station and no false operation occurs. For example,the circuit may be traced from grounded negative potential conductor 45Lconductor H8, any one of contacts Nos. 1 to 5 on contact bank D3 whileengaged by its associated wiper, conductor I29, inner lower armature andback contact of relay II'I, conductor I30 through the winding of relayH6, inner upper armature and back contact of relay I I6 through'theupper Winding of relay I I1, conductor I3I, wiper in engagement with anyof contacts Nos. 1 to 5 on contact bank As, any one of the conductorsconnected to contacts Nos. 1 to 5, respectively, for example, conductorsI32, 20!, through the winding of incoming cutthrough relay 202,conductor 203, back contact and upper armature of relay 204, conductor205, outer upper armature and back contact of relay 206, back contactand inner upper armature. of relay 201, conductor 208 to groundednegative potential conductor 45L Therefore, the applied potential oncontacts Nos, 1 to 5 on contact bank A3 meets a similar appliedpotential on conductor 208 and the incoming cut-through relay 202 doesnot operate. Similar conditions are met at each of the contacts engagedby the wiper in turn on bank A3 and the corresponding incomingcutthrough relays at each of the stations do not operate.

If the called station No." 5 is not busy, the outgoing cut-through relayIll and the incoming cut-through relay 202 will operate only after thewiper on contact bank A3 comes to rest and the slow-release relay I24releases. The operating circuits for relays I I! and 202 may be tracedfrom ground at the break contact of relay I24, conductor I20 inengagement with contact No. 5 on contact bank E3, conductor I34, innerupper armature and back contact of relay H6 through the upper winding ofrelay I ll, conductor I3I, wiper in engagement with contact No. 5 oncontact bank A3, conductors I32 and NI, through the winding of relay202, conductor 203, back contact and upper armature of relay 204,conductor 205, outer upper armature and contactof relay 200, backcontact and inner upper armature of relay 201, conductor 208 to groundednegative potential conductor 45L Busy relay I IE will not operate sinceit is of the slowoperate type and its circuit will be broken as soon asthe inner lower armature of relay I I! has left its back contact. RelayH1, in operating, locks in a circuit traceable from ground through thelower winding of relay I I1, front contact and inner lower armature ofthe relay, conductor I29, wiper in engagement with contact No. 5 oncontact bank D3, conductor I I8 to grounded negative potential conductor45L This locking circuit is required to prevent relay H'I-from releasingwhen subsequent busy tests are made on the line circuit extending fromstation No. 3. -Relay ill, in operating, disconnects at its outer upperarmature and .back contactthe upper winding of relay I02 from thetipconductor I03 of the line circuit extending .to station No. 3andprepares at its outer upper armature and front contact .a circuitextending from the .tip conductor I06 through the upper winding of relayI20. The circuit now extended through the upper winding of relay I 20 isnot established, however, until relay I23 releases. Relay 1, inoperating, also connects the ring conductor I2I which is extended overthe lower armature and back contact of relay I05, over the outer lowerarmature of relay Ill and its front contact, front contact and middlelower armature of relay II9 to the grounded negative potential conductor45L The application of groundedv negative potential to the ringconductor at this time now operates polarized relay I08. The operationof polarized relay I08 closes an obvious operating circuit extendingfrom one side of the source of alternating current I35 through thewinding of alternating current relay I09, contact and armature of relayI08, motor control contact I36, emergencystop contact I31 to the otherside of the alternating current source i35. The alternating currentrelay I09 operates and closes at its armature and contact a lockingcircuit for itself. Printer motor I38 which is connected in parallelwith the alternating current relay I09 operates at the same time thatrelay I09 operated. Relay I09 in operating disconnects dial I'I from theline circuit and connects in its place the printer set comprisingtransmitter III and receiver H2. The starting of the.teletypewritermotor is an indication to the station attendant that theconnecion has been established and the station attendant immediatelyreleases dial key IOI.

Relay II I, in operating, connects at its inner upper armature and frontcontact, conductor IIB which receives grounded negative potential fromconductor 45I to a circuit extending over the front contact and armatureof relay I23, which at this time is still operated, wiper in engagementwith contact No. on contact bank B3, conductors I49 and I33, frontcontact and lower armature of relay 202, ring conductor 200 of the linecircuit extending to stationNo. 5 through the winding of polarized relay2I0, break contact of relayZI I' to ground at the lower contact of dial2I2. The direction of current flowing through polarized relay 2I0 in thecircuit just traced is such that relay 2I0 operates to thereby operatethe motor for the printer set at station No. 5. Also, relay I I I, inoperating, disconnects at its inner upper armature and back contact thegrounded negative potential on conductor II3 from the winding of relayII3. Relay II3 will therefore release after an interval causing theoperating circuit to-relay II9 to be opened. Relay II9 will thenrelease, but by this time the printer motors at both stations Nos. 3 and5 have been started. When relay H9 releases it removes at its frontcontact and middle lower armature thegrounded .negative potential supplyfrom the ring conductor I21 and applies at its innermost lower armaturegrounded positive potential furnished over conductor 450, to the lowerwinding of relay I20, front contact and outer lower armature of relayII'I, back contact and lower armature of relay I05 to the ringconductor. Relay H9, in releasing, disconnects at its front contact andoutermost lower armature the operating circuit for stepping magnet I-22and at its back contact and outermost lower armature connects theoperating circuit for the stepping magnet I22 to the wiper of contactbank D3 for preparation of the subsequent release of the selector when adisconnect signal is transmitted. Also, relay H9 is releasing causesrelay I23 to release. Relay I23, in releasing, completes the connectionbetween the line circuits of stations Nos. 3 and 5, which circuits maybe traced from negative potential conductor 208, front contact and upperarmature of relay 202, tip conductor 2I3, break contact of dial key 2M,printer set comprising transmitter 2I5 and receiver ZIB, left-handarmature and front contact of relay 2H through the winding of polarizedrelay 2I0, ring conductor 209, lower armature and front contact of relay2232, conductors I33 and I39, contact No. 5 in engagement with the wiperon contact bank B3, armature and back contact of relay I23, through theupper winding of relay I20, front contact and outer upper armature ofrelay II'I, back contact and upper armature of relay I05, tip conductorI06, break contact of dial key IOI, printer set comprising transmitterIII and receiver H2, lefthand armature and front contact of relay I09,through the winding of polarized relay I08, ring conductor I2I, lowerarmature and back contact of relay I05, outer lower armature and frontcontact of relay II'l, through the lower winding of relay I20, backcontact and innermost lower armature of relay M9 to grounded positivepotential conductor #50. The attendant at the calling station No. 3 maynow call in the attendant at the called station No. 5 by sending Bellsignals from the teletype-writer keyboard, or send to the called stationon an unattended basis. Disconnect At the conclusion of the message,either attendant may send the disconnect signal by sending the Stopsignal code from the teletype writer keyboard. Upon receipt of thissignal the teletypewriter selecting mechanism at each of theinterconnected stations causes the motor control contact, such as I30 atstation No. 3, to open momentarily. Opening of these contacts will breakthe locking circuit for the alternating current relays such as relay I09at station No. 3 and relay 2 I I at station No. 5. The release or thealternating current relays will cause the power to be removed from theteletypewriter motors so that the motors will stop. It is to be notedthat at this time current continues to fiow over the ring side of theline circuit of calling. station No. 3 through polarized relay I08 toground at the lower contact of dial I0'I. However, the direction of theflow of current through the polarized relay is such that the relay willnot operate and the printer motor will not start again, the current flownow being due to grounded positive potential being applied to the ringconductor i2I from conductor 050. Alternating current relay I09, inreleasing, opens the tip conductor I06 and connects ground to the ringconductor lZI thereby causing difierential relay I26 to operate due tocurrent flowing in the lower winding only. The connection to the ringconductor of the called station from positive potential through thecalling station loop is cut off when relay I09 releases and relay 2I0does not reoperate. Relay 20 in operating closes at its armature andcontact an operating circuit for busy relay M0, which circuit may betraced from grounded negative potential conductor 45I, conductor lit,wiper in engagement with contact No. 5 on contact bank cut-through relay202 will be operated. There D3, conductor I29, contact and armature ofrelay I25, through the winding of relay H6, conductor i3 5, wiper inengagement with contact No. 5 on contact bank E3, conductor I28 toground at the break contact of relay I24. Relay II6 operates and looksover its inner upper armature and front contact to ground. I

Relay IS, in operating, closes a circuit from grounded negativepotential conductor 45I, conductor I I8, wiper in engagement withcontact -No. 5 on contact bank D3, conductor, I29, back contact andoutermost lower armature of relay IIS, conductor I39, through thewinding of stepping magnet I22, lower armature and front contactof relayM6, to ground at the armature of stepping magnet I22. Stepping magnetI22 having been operated during the period of the connection releasesand then reoperates with a stepping action through its own armature andback contact to restore selector No. 3 to its normal position. As soonas relay IIB operates the connection for relay 292 is broken and relay202 releases making the called station No. 5 idle and ready to acceptnew calls. Relay II! in series with relay 252, however, remains operatedthrough its lower locking winding until the selector switch at stationNo. 3 has been restored to normal. With relays H5, Ill and I28 operatedstation No. 3 circuit is held busy until the selector switch is back tonormal. This is desirable since it prevents a seizure under improperconditions of the circuit. Y

Any two of the stations may be connected in accordance with theprocedure hereinbefore described.

Power supply In order to minimize the first cost of power plant for thissystem and keep the drain small when the system is idle, a groundednegative potential rectifier 449 is furnished as a source of supply tooperate a pulsing relay, such as I02 at station 3, at any callingstation. Therefore, when the first station in the system calls, therectifier 449 furnishespower' to the loop circuit, for pulsing. Afterthe selector at the calling station has stepped to contact No. 1 thegrounded negative potential supplied over contact bank C at the callingstation to conductor 452 through the winding of control relay 453. toground. Relay 53 operates to thereby connect the alternating currentsource 454 to the motor generator sets 455. The motor generator setswill then start up and thereby furnish the loadfor the pulses, etc. Themotor generator sets will continue to run until the selector hasreturned'to normal on the receipt of a disconnect signal and if othercalls have been initiated in the meantime, they will continue to rununtilthe last selector in the system has restored to normal.

Called station busy Assuming that the called station No. 5 is busy atthe time the call is initiated at station No. 3, it may be busy undertwo different conditions, first, station No. 5 having previously calledand become connected to another station, and secondly, station No. 5having been called and connected to another station.

In the first case, the selector for station No. 5 will be in an operatedposition corresponding to the number which station No. 5112161 calledand the outgoing cut-through relay 201 will be operated. In the secondcase, station No. 5 selector will be in its normal position and theincoming are therefore two types of busy tests which the selectorcircuit of station No. 3 must be capable of making when the selectorwipers come to rest on contact No. 5 of the respective banks of selectorNo. 3.

Case 1Called station busy When the attendant at station No. 3 hasfinished dialing station No. 5, relay I02 remains operated until thenon-locking dial key IOI is released. Relay I24 will release after ashort interval, however, and establish ground on contact No. 5 whichwill be engaged by the wipers of contact bank E3. This condition closesa circuit from ground at the break contact of relay l24, conductor I28,wiper in engagement with contact No. 5 on contact bank E3, conductorI35, through the winding of busy relay I I5, back contact of inner lowerarmature of relay II'I, conductor I 29, wiper in engagement with contactNo. 5 on bank D3, conductor IIB, to grounded negative potentialconductor 45L A parallel path to the operating circuit for relay IIB maybe traced over the inner upper armature and back contact of relay H6,through the upper winding of relay II'I, wiper in engagement withcontact No. 5 on contact bank A3, conductor I32, through the winding ofincoming cut-through relay 202, conductor 203, back contact and upperarmature of relay 204, conductor 205, outer upper armature and backcontact of relay 2%, to back contact in engageable relation with theinner upper armature of outgoing cut-through relay 2M. Inasmuch as thebusy condition of station No. 5 is due to station No. 5 initiating thecall, outgoing cut-through relay 28'! will be operated and therefore thepath just described will be opened at the back contact and inner upperarmature of relay 251. The outgoing cutthrough relay Ill will thereforenot operate and relay H5 will operate and lock up to ground .at theinner upper armature. Relay H5 will remain operated until selector No. 3has stepped back to its normal position as hereinbefore described.

Case 2--Called station busy Assuming that station No. 5 has been calledpreviously by another station and is busy, the busy test is somewhatdifferent. When ground at the break contact of relay I24 is connected tothe operating circuit of relay H6 and also to the path extending overthe inner upper armature and back contact of relay IIB, through theupper winding of outgoing cut-through relay I ll,

conductor 13E, wiper in engagement with contact No. 5 of switch bank A3,conductor I52, through the winding of incoming cut-through relay 202,conductor 203, back contact and upper armature of relay 2%, conductor205, outer upper armature and back contact ofrelay 205 to the backcontact in engageable relation with the inner upper armature of relay201, as hereinbefore described, relay 251 is not operated and the pathis extended over conductor 258 to grounded negative potential conductor55 l However, since another, or a third station has already calledstation No. 5 a parallel circuit has previously been established oncontact No. 5 of switch bank A of the selector associated with the thirdstation and the outgoing cut-through relay at the third stationcorresponding to relay i H at station No. 3 has operated and locked.When relay Ill is therefore connected to this point in parallel with thecorresponding relay at the third station,

' relay will not operate since it would not receive enough current topermit its operation.

Relay H6 will therefore operate and cause the selector for station No. 3to release as described for the other busy'test.

Establishing a trunk: circuit to a public teletypzewriter exchange ofiice Assuming that station No. G is provided with equipment forestablishing a connection between any one of the stations in the privatebranch exchange offlce and a multiple switchboard'located at the publicteletypewriter exchange office, such a connection will now be describedbetween station No. 02 and the multiple switchboard at the publicteletypewriter exchange oflice. It is to be noted that the arrangementshown will permit interconnection to any one of the open line types ofteletypewriter exchange switchboard using a standard subscribers lineterminating circuit at the switchboard and a loop circuit to station No.00 through which such connection will be established. As stated above,the arrangement shown at station No. 00 will permit all the supervisoryfeatures of call, recall and disconnect in so far as the teletypewriterexchange switchboard is concerned as are provided from a regularteletypewriter exchange subscribers station associated with a publicteletypewriter exchange ofiice.

Referring to Fig. 3, the attendant at station No. 02 operates dial key30! and thereby closes a circuit extending from grounded negative sideof rectifier 449, conductor 45!, through the upper winding of pulsingrelay 392, conductor 303, back contact and outer upper armature ofoutgoing cut-through relay 393, back contact and upper armature ofincoming cut-through relay 305, tip conductor 395 of the line circuit,closed contacts of dial key 3! upper contact of dial 381, through thewinding of polarized relay 3%, lower contact of dial 38! to ground.Pulsing relay 302 operates to move its armature into engagement with itsright-hand contact thereby closing a circuit extending from negativeground potential conductor 45L conductor 309, inner upper armature andback contact of relay 3%, back contact and outer upper armature of relay3H3, conductor 3| armature and right-hand contact of relay 302, throughthe winding of relay 3 IE to ground. Relay 3|2 operates to close acircuit extending from the grounded negative potential conductor 45Lconductor 353, armature and contact of relay 3|2, through the winding ofrelay 3H5 to ground. Relay 3M corresponds to relay N9 of the equipmentassociated with station No. 3 and therefore performs functions similarto those of relay ||9 as hereinbefore described. Among these functionsis the closing of an operating circuit ferrelay 3 which extends from thenegative grounded potential conductor 551, conductor 309, inner upperarmature and back contact of relay 304, back contact and outer upperarmature of relay 3|0, conductor 3| I, upper armature and front contactof relay 3M, through the winding of relay 3 l5 to ground. Relay 3H5operates. Relay 3|5 corresponds to relay I23 of the equipment associatedwith station No. 3 and performs functions similar to those of relay I23which were hereinbefore described.

Selector switch No. 02 is now prepared to receive dial pulses. If theattendant at station No. 02 dials station No. 00 which must first. bedone before a connection can be established to the public teletypewriterexchange switchboard, the

pulsing relay 3|l2will'b'e released ten times when the'first zero'isdialed and then operate at the end of the period. When relay 302releases the first time, relay 3|6 andvv the stepping magnet 3!? willoperate in series. The operating circuit may be traced from groundednegative potential conductor 45L conductor 309, inner upright armatureand back contact of relay 3%, back contact and outerupper armature ofrelay 3| 9, conductor 3| armature and left-hand contact of relay 302,through the winding of relay 2H6, front contact and outermost lowerarmature of relay 3M, through the winding of stepping magnet 3H, lowerarmature and back contact of relay 3W, contact No. 22 engaged by thewiper on contact bank E02,, break contact of relay 3|6, to ground. Whenrelay 302 operates again the current supply will be removed' from thewinding of relay 3|6 and stepping magnet 31?. The selector magnet willtherefore step from point 22 to point I on the selector switch No. 02,but relay 3H3 being of the slow-release type will remain oper ated forthe duration of the ten successive impulses transmitted by the dial 301.

When relay 302 releases the second time the selector magnet 3|'| willagain operate, but this time-the selector wiper on bank E02 is oncontact No. 1 and'relay 3|6 is operated so the grounded operatingcircuit for the magnet is established directly through the make contactof relay 3|t and does not go through the selector bank contacts oncontact bank E02. Operation of relay 3112 the second time causes theselector switch wipers to step to contact No. 2. This sequence isrepeated during the remaining ten dial pulses, the selector wipersstepping to contact No. when relay 302 operates at the end of the seriesof pulses.

When the selector wipers reach contact No. 10 at. the end of the tenthpulse relay 3|6 releases. Relays 3| 2, 3M and 3|5, however, remainoperated since thedial key is held operated and relay 302 remains on itsright contact between the first and second train of pulses. Relays 3Mand 3|-0 remain unoperated since contact No. 10- on E02 is strapped tocontact. No. 22' only.

If the attendant at station No. 02 dials the second zero the operationsdescribed for the first train of pulses will be repeated except theselector will begin stepping. from contact No. 10 on the banks to stepII when the first pulse is received and will step: to contact No. 20when the last pulse is received.

It is to be noted that during the time the-selector' wipers arestepping, during either trainof pulses, the wiper circuit on contactb'ankBoz is held open at the outer upper armature and front contact ofrelay 304 thus preventing interference with other circuits on themultiple of that bank. The wiper on contact bank A02 has negative groundpotential applied to it during the stepping interval from contact bankD02, but this applied potential. meets a similar potential on each pointthrough the multiple for each respective stationand no false operationoccurs.

Called station N0. 00 not busy-connection established If the calledstation No. 00 is not busy, relay 384 and incoming cut-through relay 40|will operate as soon as relay 3|6 has released at the end of thetwentieth dialing pulse, the operating circuit being traceable fromground, break contact of relay 3|6, wiper in engagement with contact No.20 on contact bank E02, upper armature and back contact of relay 3 I 0through the upper winding of relay 304, wiper in engagement with contactNo. 20 on bank A02, conductors 3I8 and 3l9, through the winding ofincoming cut-through relay 40H, conductor 402, back contact and upperarmature of relay 303, conductor 404, outer upper armature and backcontact of relay 405, back contact and inner upper armature of relay406, conductor 50? to grounded negative potential conductor I. Thecircuit just traced has a path extending through the winding of relay 3l0, back contact and inner lower armature of relay 304, wiper inengagement with contact No. 20 on bank D02, conductor 309 to thegrounded negative potential conductor 45L Relay 3I0 will not operatesince it is of the slow-operate type and its operating circuit will bebroken as soon as the inner lower armature of relay 304 has left itsback contact.

When relay 304 operates it looks itself through its lower winding, frontcontact and inner lower armature, wiper in engagement with contact No.20 on bank D02 conductor 309 tothe grounded negative potential conductor45l. This locking circuit is required to prevent relay 304 fromreleasing when subsequent busy tests are made on station No. 12. Relay304' also disconnects the Winding of relay 302 from the tip conductor306 of the line circuit and prepares a circuit from the tip conductor tocontact No. 20 on bank B02 through the upper winding of relay 320. Thelatter circuit is not established, however, until relay 3I5 releases.Relay 304 also connects the ring conductor 32I of the line circuit tothe negative ground potential conductor 45I, through the front contactand middle lower armature of relay 3! 4, which relay has not as yetreleased.

Application of the negative ground potential to the ring conductor 32!causes polar relay 308 at station No. 02 to operate. When relay 308operates it closes the alternating current source 322 to thereby operatethe alternating current relay 323 and start the teletypewriter motor324. When the alternating current relay 323 operates, it looks upthrough one of its contacts. It also disconnects dial 301 and connectsthe teletypewriter comprising transmitter 325 and receiver 326 acrossthe line circuit. The starting of the teletypewriter motor is anindication to the station attendant that the connection has beenestablished. Nhen relay 304 operates it also applies grounded negativepotential on conductor 45L through conductor 309, inner upper armatureand front contact of relay 304, front contact and armature of relay 3H5,wiper in engagement with contact No. 20 on contact bank B02, conductors32? and 320, front contact and lower armature of relay 40L ringconductor 4I0, through the winding of polarized relay 408, to ground atthe lower contact of dial 409. Relay 355 has not as yet released. Sincerelay 40l is now operated so that the grounded negative potential onconductor 309 is applied to the ring conductor 4H0, polar relay 408 atstation No. 00

- operates to cause the teletypewriter motor at staand applies groundedpositive potential in its place. The operating circuit for steppingmagnet 3" is opened at the front contact and outermost lower armature ofrelay 3M and another operating circuit for the magnet is prepared at theoutermost lower armature and back contact of relay 3I4 which extends tothe wiper on contact bank D02 for subsequent release of the selectorswitch on the receipt of a disconnect signal. Relay 3I4 in releasingalso causes relay 3I5 to release. When relay 3I5 releases, the completeconnection between stations Nos. 02 and 20 is established and a loop isprovided between the two stations with positive and negative potentialapplied at opposite ends. The attendant at station 02 may now call theattendant at the called station No. 00 by sending Bell signals to theteletypewriter keyboard.

The attendant at station No. 00 upon receiving the information from theattendant at station No. 02, it being assumed that such information isthe request to establish a call to the public teletypewriter exchangeofiice, and the attendant at station No. 00, momentarily operates athreeposition key 4| I to its right-hand position, which position isidentified herein as a call-answering position. Since the teletypewritermotor M2 at station No. 00 is operating, rectifier M3 is energizedthrough the transformer 4M and the operating circuit for interconnectingrelay 4| 5 is now closed. Relay M5, in operating, closes at its innerlower armature and contact a locking circuit for itself. The attendantat station No. 02 in initiating this call by dialing station No. 00,causes the selector switch No. 02 to operate, and

the operation of this switch to effect the engagement of the wiper withcontact No. 20 on bank C02 starts the motor generator sets 455operating. The operation of motor generator'sets 455 produces positiveand negative voltages over conductors 450 and L respectively, toenergize the repeater relays P1, P2, P3 and P4 so that wheninterconnecting relay M5 is operated and locked, the trunk circuitextending to the public teletypewriter exchange office is connectedthrough the repeater circuit to the loop circuit extending throughstation No. 00 to station No.

02. A detailed description of the operation of the repeater may be hadby referring to U. S. Patent 1,601,799 granted to J Herman on October 5,1926. It is to be noted from the above brief description of theoperation of this circuit that the teletypewriter at station No. 00 isused on a monitoring basis at all times while the trunk circuitconnections to the teletypewriter exchange office are established. It isalso to be noted that the teletypewriter mechanism together with theassociated alternating current relay rectifier and interconnecting relay4I5 provided an automatic means for disconnecting the trunk circuitatthe end of a communication.

Call from public teletypewriter exchange ofiice When a call for one ofthe stations in the private branch exchange system is completed at thepublic teletypewriter exchange omce switchboard, the operator at theswitchboard operates a ringing key which connects battery tothe ringconductor 4H5 which is extended through the normally closed contact ofthe recall key 4 I I, outer lower armature and back contact of relay M5,normally closed lower left contact of key 4, condenser M3, through theringer M9 to ground. The ringing current causes the ringer M9 tooperate. To answer the call, the station ather, such as 1.

tendant at: station No. dials. aparticularnum- The dialing of 1' causesthe connection to be established between station No. 00 and station No.l in the teletypewriter private branch exchange office. Should theteletypewriter private branch exchange be connected to a teletypewriterpublic exchange office, as shown in the drawings, station No. 1 would bedifferent from the other stations in the teletypewriter private branchexchange system in that there is no teletypewriter dial or associatedequipment and no selector switch with its associated relays except inincoming cut-through relay'such as relay H15 at station No. 3. In thiscasestation No. 1 might be called a dummy. The line loop extending tostation No. 1 includes in addition to the regular resistance, not shown,a second resistance equivalent to that of a teletypewriter andassociated polarized relay. The dialing of 1 will operate selectorswitch No. 00 whereby the motor generator sets 455 will start operatingto energize the biasing windings of the repeater relays P1, P2, P3 andP4 and the operating of the teletypewriter motor at station No. 00 willenergize through transformer M4, the rectifier 413 to prepare theoperating circuit for interconnecting relay H5. The attendant at stationNo. 00 then operates the key MI to its call-answering positionmomentarily. This causes the interconnecting relay M5 to operate andlook through the front contact and inner lower armature. The operator atthe public teletypewriter exchange switchboard and the attendant atstation No. 00 may then communicate since positive and negative voltagesupplies from generator sets 455 are connected over conductors 450 and45 I, respectively, to the repeater and the teletypewriter at stationNo. 00 is connected in series between the repeater and the line circuitextending to dummy station No. l. The trunk circuit extending from theswitchboard at the public teletypewriter exchange oflice is connected tothe other side of the repeater to the cord circuit at the publicteletypewriter exchange office.

After obtaining the number of the called station desired the attendantat station No. 00 operates key M l to the left, or its Hold, positionand then sends an H signal to cause the motor of the teletypewriter atstation No. 00 to stop and the interconnecting relay 415 to release. Theconnection to dummy station No. l is also released. With key 4 in theHold position, relay 420 is connected in series with the trunk circuitand this relay therefore operates causing lamp 42! to light from source422. The lamp remains lighted as long as key Al I is in its Holdposition and there is no typing on the trunk circuit.- Typing at thepublic teletypewriter exchange office will cause the lamp to flashgiving the attendant at station No. 00 a signal that the switchboardoperator at the public teletypewriter exchange ofiice wishes torecallthe attendant at station No. 00 when the key is in the Hold position.

Following the stopping of the motor of the teletypewriter at station No.00 the attendant at that station dials the number of the called station.This operation causes the teletypewriters at the called station andstation No. 00 to start, that is, the motors for the teletypewriters tostart. The attendants at the called station and station No. 00 may nowcommunicate and following this the attendant at station No. 00 connectsthe line circircuit to the trunk circuit by releasing key 4H from. itsHold position and momentarily oper' ating it to the call-answeringposition. Interconnecting relay 4! 5- then operates and locks and thethrough connection is established between the public teletypewriterexchange switchboard and the 'teletypewriter at the called station.

If after the communication is established the attendant at the calledstation wishes to recall the, operator at the public teletypewriterexchange switchboard, he may do so by sendingS (bell) signals. Thesesignals will recall the attendant at station No. OO'Who in turn mayrecall the switchboard operator at the public teletypewriter'exchangeoffice by operating the recall key ill.

When the called station has completed the communication, he willdisconnect by sending an H signal which will causethe teletypewritermeters at the called station and at station No. ()0 to'stop.

ie rectifier- 4l3=will deenergize and the interconnecting relay 4! 5will release. This release will automatically cause a disconnect signalto be transmitted to the public teletypewriter exchange oifice becausethe loop to that office will become open and one side will be groundedthrough the normally closed upper left-hand contacts of key 4| I whilethe other will be connected to the ringer 4 Hi;

What is claimed is:

1.,A signaling system comprising a switching center, outlying stations,normally open circuits for respectively connecting said outlyingstations to said switching center, means at each of said outlyingstations for closing its associated circuit, impulse transmitting meansand a code combination signal transmitting and receiving device at eachof said outlying stations, a rotary selector switch and equipmentassociated therewith individual to each of said stations and responsiveto said impulse transmitting means at its associated station whereby anystation, when said impulse transmitting means thereat are operated, maybe connected with any other idle station.

2. A signaling system according to claim 1 wherein the equipment at oneof said outlying stations includes a trunk circuit for extending anoutgoing call from any one of said outlying stations to points outsidethe system and an incoming call to any one of said outlying stationsfrom points outside the system.

3. A communication system comprising a switching center, outlyingstations, normally open circuits for respectively connecting saidoutlying stations to said switching center, a central oiiice, a maincircuit interconnecting one of said cutlying stations and said centralonice, impulse transmitting means and a teletypewriter signaltransmitting and receiving device at each of said outlying stations,aselector switch and equipment associated therewith individual to eachof said stations and. responsive to said impulse transmitting'means atits associated station and a common power supply for said impulsetransmitting means, said selector switches and their respectivelyassociated equipment comprising means'responsive whereby any one of saidoutlying stations may be connected to any other idle outlying station orto said central oifice as desired. p

4. A communication system in accordance with claim 3, wherein theequipment associated with tions, when said associated outlying stationis engaged in an established connection, means for operating one of saidrelays when said associated outlying station originates the call for theestablished connection other means for operating the other when saidassociated outlying station answers the call.

5. A communication system according to claim 3 wherein the selectorswitches and the equipment respectively associated therewith comprisemeans for simultaneously establishing connections between two or morepairs of outlying stations individually, the connect-ion between thestations of any one pair being established independently of a connectionsimultaneously established between stations of any other of said pairsof stations.

6. A communication system in accordance with claim 3 wherein thetransmitting and receiving devices at each of said outlying stations areteletypewriters having driving motors individual thereto and meansarranged, when any two of said teletypewriters are interconnected forcommunication, to be controlled from either of the two interconnectedteletypewriters.

'7. A communication system in accordance with claim 3, wherein one ofsaid outlying stations comprises signaling equipment for supervising aconnection between any one of said outlying stations and said centraloifice, said connection including said main circuit.

8. A communication system in accordance with claim 3 wherein said commonpower supply comprises means for normally maintaining it in an idlecondition and in response to the operation of said selector switch to beautomatically controlled to establish a connection between any two ofsaid outlying stations or between one of said outlying stations and saidcentral office for the duration of such a connection and to complete adisconnection of such connection at the conclusion of a communication.

9. A communication system in accordance with claim 3 wherein said maincircuit comprises means at said one of said outlying stations forconnecting any one of the other of said outlying stations through saidone outlying station, and said signal transmitting and receiving deviceat said one of said outlying stations comprises means for monitoring thecommunication be tween any one of said other outlying stations and saidcentral ofiice.

10. A teletypewriter system comprising,outlying stations, a selectorswitch and equipment associated therewith individual to each of saidstations, a switching center whereat said selector switches and saidequipment are located, normally open circuits for respectivelyconnecting each of said stations with said switching center, a callinitiating device at each of said outlying stations for conditioning foroperation its associated selector switch, a pulse transmitting dial ateach of said outlying stations for operating its associated conditionedselector switch, a signal transmitting and receiving device and drivingmeans therefor at each of said outlying stations, a common source ofpower supply at said switching center for furnishing power to initiate acommunication connection between said outlying stations in response tothe operation of a call initiating device, an amplifying devicecontrolled by said pulse transmitting dial and said common source ofsupply for completing said connection, starting said driving means atthe signal transmitting and receiving devices at interconnectedstations, for transmitting signals between the transmitting andreceiving devices at interconnected stations, for transmittingsupervisory signals and for restoring said driving means and saidoperated selector switches to normal at the conclusion of acommunication.

11. A teletypewriter system in accordance with claim 10, wherein saidamplifying device is common to said outlying stations and said switchingcenter for providing grounded positive potentials and grounded negativepotentials to opposite ends, respectively, of said normally opencircuits interconnected in an established connection.

12. A teletypewriter switching system comprising a plurality of lines, acentral switching point including stepping devices for connecting anytwo of said lines together for intercommunication, a source of power forcausing any one of said devices to step, a normally idle auxiliarysource of power for devices controlled by any step from normal of any ofsaid stepping devices to render operative said auxiliary source ofpower, and connections whereby said auxiliary source of power furnishesenergy for controlling further stepping of said devices.

13, A teletypewriter switching system comprising a plurality of lines, acentral switching point including stepping devices for connecting anytwo of said lines together for intercommunication, a source of power forcausing any one of said devices to step, a normally idle auxiliarysource of power for devices controlled by any step from normal of any ofsaid stepping devices to render operative said auxiliary source ofpower, and connections whereby said auxiliary source of power furnishesenergy for telegraphic impulse transmission between any two of saidlines connected by said stepping devices.

FRED J GEN SINGER.

